Airborne surveys measuring the earth's magnetic field, resistivity or other electomagnetic properties, or gamma ray emission over parts of North America.

Measurements of in-situ magnetic properties of several map units to determined whether or not mapped lithologies were responsible for aeromagnetic anomalies observed in a previous high-resolution survey (data of Sweeney, 2000).

Surveys originally carried out by Soviet geophysicists from 1972 through 1974 were digitized. Georeferencing was problematic as were some of the measured characteristics; we explain what we did and how we have understood these data.

Gravity station data and physical property measurements used to infer subsurface geologic structure

Major assessment of the environmental effects of historical mining in the Animas River watershed with GIS data files, tables, and plates.

Explanation of the Earth's magnetic field and how USGS measures it. Defines magnetic anomaly, induced and remanent magnetism in rocks, and describes magnetic anomaly maps.

Database includes new helicopter aeromagnetic data, point locations of the local maximum horizontal gradient derived from the aeromagnetic data, and physical property data.